1. Field of the Invention
This invention relates to Y.sub.2 O.sub.3 :Eu phosphors, and more particularly relates to such phosphors containing MgO and having increased brightness.
2. Prior Art
During the early development of the modern shadow mask tri-color cathode ray tube for color television, a chief problem was poor brightness, since about 85 percent of the beam current was masked and thereby not available to provide excitation energy to the screen. With the introduction of the "all-sulfide" color tube about 1961, (see U.S. Pat. No. 2,991,383, issued to A. E. Hardy, July 4, 1961) some improvement was realized in this and other regards. However, such a tube still had marginal brightness and other shortcomings. In June of 1964, the "rare earth" tube, that is, a tube employing a Eu-activated rare earth red phosphor, was introduced. See Television Digest, Vol. 4, No. 23, p. 7, June 8, 1964. Such a tube exhibited improved white brightness, increased linearity of color response, and increased linearity of brightness, and as a result enjoyed remarkable commercial success. See The Wall Street Journal, May 12, 1965, page 1; and Chemical and Engineering News, June 12, 1967, pp. 46-68. Of three early examples of the rare earth red phosphor; yttrium oxide (Y.sub.2 O.sub.3 :Eu), yttrium oxysulfide (Y.sub.2 O.sub.2 S:Eu), and yttrium orthovanadate, (YVO.sub.4 :Eu), Y.sub.2 O.sub.3 :Eu is presently preferred by some for its greater brightness and freedom from sulfur, the presence of which could lead to handling, recovery and/or disposal problems. Over the years, various techniques have been employed to improve the Y.sub.2 O.sub.3 :Eu phosphor. See U.S. Pat. Nos.: 3,759,835 and 3,574,131 (process for making); 3,582,493 and 3,635,658 (control of particle size; 3,637,517 and 3,684,546 (control of purity); 3,619,265 and 3,740,250 (improved screen adherence; 3,607,371 (increased bulk density); 3,574,130 and 3,830,748 (control of brightness); 3,870,650 (improved crystallinity); 3,711,418 (control of decay time); and 3,676,177 (process for screening), all assigned to the present assignee. Efforts to further improve this phosphor hold the promise of improved color tube performance.